Three events for the decay K + → π + vv have been observed in the pion momentum region below the K + → π + π 0 peak, 140 < P π < 199 MeV/c, with an estimated background of 0.93 ± 0.17(stat.) +0.32 0.24 (syst.) events. Combining this observation with previously reported results yields a branching ratio of B(K + → π + vv) = (1.73 +1-15 -1.05 ) X 10 -10 consistent with the standard model prediction.
